Within the field of packaging of liquid products deaeration is a well established concept and deaeration is included as an essential step in most processing plants e.g. in plants where liquid product is received as a bulk in a first end of the line and delivered as individual packaging containers in the other end of the line. Air (or oxygen) may be present in the liquid product for different reasons, the two main reasons being that it is dispersed or dissolved. Taking the example of milk, there will be some oxygen in the milk already before it has left the cow, and more oxygen will be mixed and dissolve into the milk at each processing step starting with the milking process itself.
The air and oxygen may result in several negative effects ranging from reduced skimming efficiency in separators, cavitation in the product during processing, fouling of heating surfaces in pasteurizers, shortened product shelf life (due to oxidation), etc., which are some reasons to why deaeration is a well-established processing step.
To simplify the underlying theory, which obviously is well-established and well-known to the skilled person, the solubility of a gas such as oxygen or nitrogen in a liquid will depend of temperature and pressure. At lower temperatures more oxygen or nitrogen may be dissolved in the liquid than what is the case at a higher temperature, i.e. the saturation concentration is higher at a lower temperature. For pressure the relationship is reversed, the higher the pressure the higher the saturation concentration. This simple relationship establishes that in order to deaerate a liquid one or both of the temperature or the pressure may be altered. Also, it may be obvious that deaeration as such is not difficult to accomplish by simply dialing in the desired temperature and pressure of a particular saturation concentration in a vessel containing the liquid. In a commercial production line, however, the deaeration should allow treatment of thousands of liters of liquid product per hour with a requirement of being energy efficient which renders the theoretical approach of awaiting equilibrium to be reached inapplicable.
A deaeration method more commonly used in the main field of the present invention is to make use of a vacuum deaeration in an expansion vessel connected to vacuum. The liquid is transported to the expansion vessel with a certain temperature which is some degrees above the boiling point at the pressure prevailing in the expansion vessel. When the liquid enters the vessel via a valve and the temperature and pressure conditions in the vessel causes it to instantly start boiling, a process referred to as flash boiling (flash or flashing in the following). The process results in that liquid in vaporized and that air is released from dissolved form during flashing. Liquid vapor condense against cooled areas in the vessel, while the released air is evacuated from the vessel by the vacuum pump, while the liquid exits through an opening in the bottom of the vessel. In order to increase the separation rate the liquid may enter the expansion vessel in a tangential direction, so as to induce a swirl.